Ordinary liquid developing agents for electrostatic photography are agents in which an organic or inorganic pigment or dye such as carbon black, nigrosine or phthalocyanine blue, etc. and a natural or synthetic resin such as an alkyd resin, acrylic resin, rosin or synthetic rubber, etc. are dispersed in an aliphatic petroleum hydrocarbon or similar highly insulating, low permittivity liquid and which are further given addition of a polarity control agent such as a metal soap, lecithin, linseed oil, a higher fatty acid or vinyl pyrrolidone, etc.
The resin in such developing agents is dispersed in the form of insoluble latex grains with a diameter of several nanometers to several hundred nanometers, and in a conventional liquid developing agent a soluble resin for dispersion stabilization and a polarity control agent are in a state in which they are easily dispersed in the solution since there is imperfect bonding between them and the insoluble latex grains. Consequently, there is the drawback that on long-term storage or repeated use the soluble dispersion stabilization resin becomes detached from the insoluble latex grains, the grains precipitate, aggregate and accumulate and the polarity becomes unclear. Further, since it is difficult to re-disperse the grains once they have aggregated and accumulated, the grains remain adhering everywhere to the development unit, so leading to staining of image portions and development unit problems such as solution feed pump blockage, etc.
A means which has been proposed for making improvement with respect to this drawback and has been disclosed in U.S. Pat. No. 3,990,980 is to bring about chemical bonding of the soluble dispersion stabilization resin and insoluble latex grains. However, although the dispersibility stability with respect to the natural precipitation of grains is improved to some extent in such a liquid developing agent, it is still unsatisfactory and when the developing agent is put into and used in an actual development apparatus there are the drawbacks that toner adhering to various portions of the apparatus hardens as a film, re-dispersion is difficult and apparatus malfunction and staining of images, etc. are caused and there is insufficient re-dispersibility for practical purposes. In the above-noted procedure for manufacture of the grains, if monodisperse grains with a narrow grain size distribution are expected to be produced, there are great restrictions with regard to the combinations of dispersion stabilization agent used and the monomer to produce insolubilized polymer. Further, in the above-noted procedure for manufacture of the grains, grains with a broad grain size distribution comprising a large amount of coarse grains or polydisperse grains in which two or more average grain diameters are present are produced. Also, since it is difficult to achieve a required average grain size in monodisperse grains with a narrow grain size distribution, large grains of 1 .mu.m or more or very fine grains of 0.1 .mu.m or less are formed. There have also been the problems such as the fact that the dispersion stabilization agents used have to be manufactured by going through complex and time-consuming manufacturing stages.
JP-A-60-185962 and JP-A-61-43757 (the term "JP-A" as used herein means an "unexamined published Japanese patent application") disclose methods wherein, in order to provide improvement with respect to these drawbacks, the degree of dispersion, re-dispersibility and storage stability of grains are improved by producing insoluble dispersion resin grains by polymerizing the monomer in the presence of a polymer for which a bifunctional monomer has been used or a polymer for which a macromolecular reaction has been used.
Another aspect is that in recent years, methods of printing a large number of sheets, 5000 or more, using a master plate for offset printing by an electronic photographic system have been tried and particular advances have been made in improvements of master plates with the result that it has become possible to print 10,000 or more large-size sheets. Progress has also been made in connection with shortening of work times in electronic photographic plate making systems and improvements have been made with respect to speeding-up of development stage to fixing stage.
With dispersed resin grains manufactured by the means disclosed in the above-noted JP-A-60-185962 and JP-A-61-43757, there is still failure to always achieve satisfactory performance with respect to dispersibility and re-dispersibility of the grains when the speed of development is increased or with respect to press life (printing durability) in the case of large-size (e.g., size A3 or larger) master plates.
The present invention resolves the above-noted problems associated with conventional liquid developing agents.
It is an object of the invention to provide a liquid developing agent with which there is excellent dispersion stability, re-dispersibility and fixing characteristics even in an electrostatic photographic plate making system in which the steps of development step to fixing step are made fast and large-size master plates are used.
It is another object of the invention to provide a liquid developing agent which permits production of original offset printing plates with excellent printing ink receptivity and durability in printing.
It is a further object of the invention to provide a liquid developing agent which in addition to the above-noted applications is suitable for various types of electrostatic photography and various types of transfer applications.
Yet another object of the invention is to provide a liquid developing agent which is employable in all systems which can use liquid developing agent such as systems for ink jet recording, cathode ray tube recording and pressure change, static electricity change or similar change process recording. The use is described, for example, in Kiroku-Zairyo to Kankosei-jushi (Recording Materials and Photosensitive Resin), edit. by Shinohara et al. published by Gakkai Shuppan Center (October 1979).